Method, system and calibration technique for power measurement and management over multiple time frames

ABSTRACT

A method and system and calibration technique for power measurement and management over multiple time frames provides responsive power control while meeting global system power consumption and power dissipation limits. Power output of one or more system power supplies is measured and processed to produce power values over multiple differing time frames. The measurements from the differing time frames are used to determine whether or not system power consumption should be adjusted and then one or more devices is power-managed in response to the determination. The determination may compare a set of maximum and/or minimum thresholds to each of the measurements from the differing time frames. A calibration technique uses a precision reference resistor and voltage reference controlled current source to introduce a voltage drop from the input side of a power supply sense resistor calibration is made at the common mode voltage of the power supply output.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to previously-filed co-pending U.S.patent application Ser. No. 10/727,320, filed on Dec. 3, 2003 andentitled “METHOD AND SYSTEM FOR POWER MANAGEMENT INCLUDING LOCALBOUNDING OF DEVICE GROUP POWER CONSUMPTION”, which is assigned to thesame assignee. The specification of the above-referenced patentapplication is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to power management inprocessing systems, and more particularly, to a power management schemethat uses multiple time frame power measurements to estimate powerconsumption changes and control system power consumption.

2. Description of the Related Art

Present-day computing systems include sophisticated power-managementschemes for a variety of reasons. For portable computers such as“notebook”, “laptop” and other portable units including personal digitalassistants (PDAs), the primary power source is battery power.Intelligent power management extends battery life, and therefore theamount of time that a user can operate the system without connecting toa secondary source of power. Power management has also been implementedover “green systems” concerns so that power dissipated within a buildingis reduced for reasons of energy conservation and heat reduction.

Recently, power management has become a requirement in line powerconnected systems, particularly high processing power cores and systemsbecause the components and/or systems are now designed with totalpotential power consumption levels that either exceed power dissipationlimits of individual integrated circuits or cabinets, or the totalavailable power supply is not designed to be adequate for operation ofall units simultaneously. For example, a multiprocessing system may bedesigned with multiple subsystems, but have a power supply system thatcannot supply the maximum potential power required by each subsystemsimultaneously. In another example, a processor may be designed withmultiple execution units that cannot all operate simultaneously due toeither an excessive power dissipation level or a problem in distributingthe requisite current level throughout the processor without excessivevoltage drop. The potential power available from a power supply does nothave a single value, but typically is a relationship between power leveland time in which greater power is available for shorter intervals up toa maximum power level beyond which the power supply will fail at anypower level (either due to protection circuitry or absolute failure suchas an over-current in a voltage-regulating device).

Typically, information about changes in power consumption within asystem is provided by either a static power measurement determined fromcurrent sensing and/or by thermal measurements that relate theaccumulation of heat within the system to power consumption. Neither aresufficiently accurate for fine-grained power management schemes. Powermanagement schemes requiring fine-grained power consumption information,such as that disclosed in the above-referenced Patent Application eithermeasure current consumption at a fairly slow rate, or estimate powerconsumption based on calculations made in conformity with the powersavings state of each device in the system. Current measurements lackaccuracy in that they do not take into account the instantaneous voltageof the system power supply, which affects the accuracy of any power usecalculation. Also, estimations based on device status are onlyapproximations to the actual power consumed by the system. Even at thedevice level, the approximation is seldom accurate, as estimates ofpower from device or system load calculations or based on a total ofactivated sub-units do not accurately reflect the actual powerconsumption of the system. Further, the typical long term measurementsmade by the power subsystem are typically provided for control ofthermal or current failure conditions and do not provide sufficientinformation for controlling short term variations in power consumption.Therefore, more power may actually be available in the short term thanis actually used, or if the system is operated close to the powermargin, short-term behavior may cause the system to exceed desiredoperating power levels.

Power supply current measurements are also generally inaccurate for thepurposes of fine-grained power management. In particular, currentmeasurements made through a small voltage drop introduced at the outputof a power supply are typically difficult to calibrate accuratelywithout interrupting the power supplied to the system.

It is therefore desirable to provide a method and system for providingpower management within a processing system in response to a moreaccurate measurement of system and device power consumption thatreflects both short term and long term constraints so that system poweruse may be optimized. It would further be desirable to provide a methodand apparatus for calibrating the power measurement without interruptingpower to the system.

SUMMARY OF THE INVENTION

The objective of providing power management within a processing systemresponsive to fine-grained power measurements is provided in a methodand system for power measurement and management. The objective ofcalibrating the measurement without interrupting system power isprovided in a method and apparatus for calibrating a power measurement.

The method and system for power management measure power supplied by oneor more power supplies over multiple time frames of differing lengthsand then adjusting the system power consumption in response to themeasurements. The measurements can then be compared to multiplethresholds in order to determine whether or not the system power isexceeding permissible consumption levels for any of the time frames.Alternatively, or in concert, measurements may also be compared tominimum thresholds so that system operation can be optimized when somein-demand devices are being power-managed. The method may be performedat the sub-unit level, by effectively measuring power consumption andbounding it at each device among multiple devices. Alternatively, themeasurements may be conducted at the system or device level andcommunicated to a global power management algorithm that thenpower-manages the entire system.

The power management hardware and/or software uses each one of aplurality of filters to determine the power supply current and voltagefor each time frame and may be implemented by an A/D converter andfiltering algorithms. The A/D converter is preceded by an anti-aliasingfilter to improve accuracy of the measurements by removing frequencyinformation greater than the Nyquist rate from the power supply voltageand current measurements.

The calibration of the voltage measurement(s) is accomplished bymeasuring a precision voltage source. The calibration of the currentmeasurement(s) is accomplished by generating a known voltage drop via aprecision reference resistor and a precision current source controlledby the precision voltage source. The voltage drop is generated from theinput node of the power supply sense resistor as is the currentmeasurement voltage drop, so that the current calibration measurement ismade differentially across the reference resistor while the actualcurrent measurement is made differentially across the power supply senseresistor. The same anti-aliasing filters and A/D converters are used inthe calibration process, so that any non-linearity and offset in thesystem at the common mode voltage are taken into account. The resultingmeasurements thus have the same common mode voltage at the senseresistor input node and can have a common mode voltage matched forprecision at the second measurement node by selecting the current sourceand reference resistor appropriately.

The foregoing and other objectives, features, and advantages of theinvention will be apparent from the following, more particular,description of the preferred embodiment of the invention, as illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives, and advantages thereof,will best be understood by reference to the following detaileddescription of an illustrative embodiment when read in conjunction withthe accompanying drawings, wherein like reference numerals indicate likecomponents, and:

FIG. 1 is a block diagram of a computing system in accordance with anembodiment of the invention.

FIG. 2 is a block diagram depicting a power supply measurement circuitin accordance with an embodiment of the present invention, includingcalibration circuits in accordance with another embodiment of thepresent invention.

FIG. 3 is a block diagram depicting a power measurement unit inaccordance with an embodiment of the present invention.

FIG. 4 is a flowchart depicting a method in accordance with anembodiment of the present invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENT

The present invention concerns a technique for power management thatrelies on power supply current and voltage measurements to accuratelymeasure power consumption of individual devices or an entire system andadjust power management settings up and/or down in conformity with themeasurements. A novel measurement scheme provides power consumptioninformation over multiple time scales by filtering (e.g., integrating)the current and voltage waveforms over multiple differing predeterminedperiods. The multiple time scale measurements provide for optimum use ofavailable power and avoidance of power supply overload conditions foreach time frame.

Referring now to FIG. 1, a processing system is depicted in accordancewith an embodiment of the present invention. Processing subsystems10A-10D illustrate identical sub-units of the overall system, andinterconnection between processing subsystems 10A-10D is not detailed,nor are connections to peripheral devices. However, it should beunderstood that such connections and devices generally exist inprocessing systems and that the techniques of the present invention canbe applied to peripheral devices within an processing system as well aselectronic systems in general.

A power supply unit (PSU) 16 provides power to processing subsystems10A-10D and may comprise more than one power supply unit operating intandem or may supply power to separate partitions of the system. A powermeasuring unit 12 is shown within PSU 16 as well as other measuringunits 12A located within processing subsystem 10A. Sense devices(generally resistors) 18 and 18A provide power measuring units 12 and12A with a measure of the current consumed either by the system (viasense device 18) or individual subsystems or device (via sense devices18A). Sense devices 18 and 18A are shown separately to illustrate thehigh-side power supply connections to the subsystems (the power supplyreturn paths are not shown). Measuring unit 12 will generally not beused if the distributed measuring units 12A are present, but is shownfor completeness, as power measurements can be conducted at any level aslong as they present a complete picture of either the total system powerconsumption that must be bounded, or of a local power consumption usedto enforce a local bound such as that imposed by the above-incorporatedPatent Application. Thus the techniques of the present invention can beused in conjunction with the techniques disclosed in theabove-referenced patent applications, providing a mechanism by whichlocal bounding of device power consumption can be enforced and optimizedover differing time scales.

Control of power consumption can be effected in a variety of manners.Within this application, reference to a “power-managed device” includesnot only devices that change power consumption in response to powermanagement commands, but devices or subsystems that include discretepower control electronics that isolate power supply lines from thedevices or subsystems, or power supplies that supply subsystems that areresponsive to commands or signals to disable primary output power. Localpower management units (PMUs) 14A are illustrated within processingsubsystems 10A to show the control path from the measurement units 12Ato a destination that can adjust power consumption in response to themeasurements of the present invention, and will generally be a processorand program instructions that provide power management in response toinformation received from measurement units 12A or measurement unit 12.However, in the alternative or in combination, information frommeasurement units 12A or measurement unit 12 can be sent to a global PMU14 that controls device power management states from a top-downperspective. Generally, global PMU 14 is either operating system or BIOSprogram instructions that may be executing on any processor withinprocessing subsystems 10A or another processor coupled to the depictedsystem. However, hardware implementations of global PMU 14 arecontemplated for use within the system of the present invention, forexample when a hardware controller controls banks of individual powersupplies each for providing power to a subsystem or controls throughsignaling the power management state of multiple subsystems. In thatexample, the global PMU 14 signals the individual devices or powersupplies to affect power management.

Generally, both global PMU 14 and local PMUs 14A will be used in asystem if local control is provided at all, because if all informationand power use and control of power management states is contained at alocal level, then only local bounding is supported and the total systempower supply cannot be used in an optimal manner. For this reason, thepresent invention provides not only local multiple time-frame powerwaveforms for power consumption analysis and control, but sends eitherthe waveform information directly or a composite function of thewaveform information to global PMU 14. Global PMU 14 might not provideany direct power management control, but can adjust local bounds of eachprocessing subsystem to optimize use of available power from PSU 16.Alternatively, or in concert, Global or local PMUs 14 and 14A mayrepresent operating system or processor control functions such as thescheduler that affect power management control via scheduling more orless threads for a given processor, adjust CPU operating frequency,disable execution blocks within a processor or any other mechanism bywhich power management within a device or processor is effected. Assuch, the terminology “adjusting a power management state” should beunderstood to include the above techniques and should not be construedas limited to a particular power management command structure.

Referring now to FIG. 2, a power measurement circuit in accordance withan embodiment of the invention including calibration circuits inaccordance with another embodiment of the invention is shown. A 12Vpower supply input is received at PMU 22 through sense resistor Rs. Theinput side of sense resistor Rs is also connected to a differentialamplifier Al. A selector 24A selects between the output terminal ofsense resistor Rs and the output of a current measurement calibrationcircuit, so that when a Calibrate/Measure signal supplied by a serviceprocessor 29 is in the Calibrate state, the current measuring circuit iscalibrated by measuring the voltage drop generated across a referenceresistor Rr by a precision current reference formed by transistor Q1resistor Rv, amplifier A2, zener diode VR1 and resistor R1. The currentdrawn through resistor Rr forms part of the power consumption of thedevice in which PMU 22 is located, and therefore should be a smallcurrent that does not reduce available power and resistor Rr is scaledso that the voltage drop across Rs and Rr are approximately equal undernominal operating conditions. The calibration of the current measurementcircuit at the common-mode voltage of the power supply output (ratherthan at a particular voltage reference corresponding to the voltage dropacross Rs as is typical) provides a calibration value free ofnon-linearity error at the common-mode voltage of the power supply,which can be substantial when amplifier A1 and selector 24A areoperating near their own power supply rails (e.g., when no highervoltage source is available to power the measurement circuits).

A voltage measurement portion of PMU 22 is provided through selector 24Bwhich selects between a divided version of the power supply voltageprovided by resistors R2 and R3 when the Calibrate/Measure signal is inthe measurement state, and the reference voltage produced acrossresistor Rv when the Calibrate/Measure signal is in the calibrationstate. Both the voltage and current calibration or measurement signalsare provided to the inputs of corresponding anti-aliasing filters 26Band 26A which removes harmonics from the power supply at greaterfrequency than the Nyquist rate (f_(s)/2) and either the voltage or thecurrent waveform is selected as input to an analog-to-digital converter(ADC) 28. Service processor 29 then accumulates samples of both currentand voltage waveforms, adjusts them by the calibration values obtainedduring periodic calibration intervals and provides filtering of thecurrent and voltage waveforms according to multiple time-scales. Inpractice, the filtering algorithm may be an unweighted averagingalgorithm or more sophisticated weighted filters and feedback-baseddigital filtering may be employed. Low pass filters or bandpass filtersmay be employed for the time-frame filters, although the longest timeframe filter will generally-have a low pass characteristic. The use ofbandpass filters would provide only relative change information in powerconsumption rather than absolute power consumption during thecorresponding time frame, which complicates computation and is thereforegenerally not preferred.

The filtered current and voltage waveforms corresponding to each timeframe are then multiplied together to determine the actual powerconsumption of the device or system in each time frame. A set of threefilters having time-scales of 1 ms, 60 ms, and 1 sec. has been testedand shown to provide adequate responsiveness to power consumptionchanges. However, any number of filters and waveforms may be used inaccordance with the behavior of the system and the power supplies.Service processor 29 uses the power waveforms computed above todetermine whether or not to adjust the power management state of one ormore devices in the system. The devices are generally downstream of thepower measurement, but this is not a limitation of the invention, asinformation about power consumption in one partition of the system isrelevant to overall power consumption, and thus information about powerconsumption in one partition may be used to adjust power managementlevels in another. For example, in a system where the power managementis increasing online availability of resources in response todetermining that the demand-based power consumption of a particulardevice is lower than its budget, the system may then increase theresource availability in another device.

In the exemplary embodiment, service processor 29 compares eachtime-frame power waveform with a maximum and minimum threshold andeither performs power management control directly or communicates powermanagement information to another unit, operating system or BIOS inorder to effect power management in response to the comparisons. Themultiple time-frame comparisons provide the power management scheme withthe ability to use short-term higher levels of power than would bepossible with a single time frame scheme. The multiple time-framecomparisons also provide a responsiveness that is typically higher thanany thermal or normal power measurement so that changing conditions thatmay result in a failure may be detected quickly and averted.

Referring now to FIG. 3, a power measurement unit in accordance with anembodiment of the invention is illustrated. The illustration provides afunctional level description that may be implemented in analog, digitalor switched-capacitor hardware, or may be implemented by a processorexecuting program instructions, such as service processor 29. Theoutputs of current measurement circuit 40A and voltage measurementcircuit 40B are applied to sets of respective filters 42A-C and 42D-Fthat provide the multiple time-frame waveforms. A set of multipliers46A-C then multiply the current and voltage waveforms to provide inputsto a comparison unit 44 that compares the time-frame power waveforms tomaximum and/or minimum thresholds. Comparison unit 44 suppliesinformation to local and/or global PMUs so that system and/or devicepower consumption can be adjusted in response to the comparisons.

While the figure provides a concrete example of an architecture thatimplements the above-described power waveform computation andcomparison, the depicted architecture should not be construed aslimiting. For example, the filtering may be performed after a singlemultiplication of the outputs of current measurement circuit 40A andvoltage measurement circuit 40B and the comparison unit may provide amore complex treatment of the resulting filtered power waveforms as afunctional relationship between the power consumption trend and maximumand/or desired minimum power consumption. Alternatively also, the filtersets 42A-C and 42D-F may be sets of cascaded filters, with the shortesttime-frame filter located first in the cascade and so forth.

Referring now to FIG. 4, a power management method in accordance with anembodiment of the invention is depicted in a flowchart. First,calibration values for current and voltage measurements are taken (step40) and maximum and/or minimum power consumption bounds for each timescale are determined (step 42). Current and voltage are then measured ateach time-frame and power waveforms are calculated (step 44). Each timeframe waveform is compared with the minimum and/or maximum constraints(step 46) and then if the power use is out of bound for a particulartime scale (decision 48) the power management level of a device ordevices is adjusted in conformity with the bounds comparison (step 50).The current and voltage measurement, power computation and comparisonsare then repeated until the scheme is ended or the system is shut down(step 52).

While the invention has been particularly shown and described withreference to the preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in form,and details may be made therein without departing from the spirit andscope of the invention.

1. A method of managing power in an electronic system, comprising:measuring a current and a voltage supplied to said at least a portion ofelectronic system; computing a power waveform from said current and saidvoltage and filtering said power waveform to produce multiple time-framemeasurements for multiple time-frames of operation of said electronicsystem, wherein said multiple time-frames are all of differing lengths;comparing said multiple time-frame measurements with a correspondingpair of predetermined thresholds including a minimum threshold and amaximum threshold for each of said multiple time-frames, to determinewhether at least one of said multiple time-frame measurements indicatesa need to adjust power consumption within said electronic system; andcontrolling a power management state of at least one component withinsaid electronic system, wherein in response to said comparingdetermining that a particular one of said multiple time-framemeasurements exceeds said corresponding maximum threshold, saidcontrolling controls said power management state to reduce powerconsumption for a particular time frame corresponding to said particularone of said multiple time-frame measurements, and wherein in response tosaid comparing determining that said particular one of said multipletime-frame measurements falls below said corresponding minimumthreshold, said controlling controls said power management state toincrease power consumption for said particular time frame.